Spartina Alterniflora

Where did Spartina Alterniflora come from?

Spartina alterniflora, also known as giant cordgrass or smooth cordgrass, is native to the Gulf of Mexico and East Coast wetlands of the United States. The plant was intentionally introduced to countries such as Great Britain, France, The Netherlands, New Zealand and China because of its ability to control erosion.

The plant was unintentionally introduced to the Pacific Coast of the United States along Washington, Oregon and California, between the late 19th century and early 20th century. Seeds may have come in oyster barrels shipped from the East Coast or from packing material, which used the plant to protect cargo in ship holds. The original introduction continues to be disputed though.

Spartina alterniflora, USDA
Spartina alterniflora | USDA

Where and How It Spreads

There are an estimated 1,000 patches of Spartina alterniflora spreading from Puget Sound in Washington down to the San Francisco Bay area. These include places such as: Alameda Island, Hayward Marsh, San Francisco Bay National Wildlife Refuge and San Bruno Slough in California; Siuslaw River estuary in Oregon; Willapa Bay, Grays Harbor, the Copalis River Estuary, Padilla Bay and Whidbey and Camano islands in the Strait of Juan de Fuca in Washington.

Washington’s largest population of Spartina alterniflora is in Willapa Bay, where it covers an estimated 15,000 to 25,000 acres. The Spartina alterniflora population is spreading at a rate of about 20 percent annually.

 Ecological Impacts

Although Spartina alterniflora is valuable in its native range, when it is introduced into the mudflats and salt marshes of West Coast ecosystems it becomes invasive and damages the native habitat. These West Coast ecosystems do not have the same insects found in the plant’s native range, which feed on the plant and control its spread.

Plant communities such as pickleweed, seaside arrow-grass, fleshy jaumea, eel grass and the alga, Fucus distichus are being overtaken.

Loss of mudflat habitat causes ecosystem changes that negatively impact marine species such as the juvenile chum salmon, Dungeness crab and English sole that rely on these habitats as ample food sources.

Commercial oyster production in Willapa Bay has been threatened because mudflat culture beds are being invaded. Also, at the Willapa National Wildlife Refuge, it has displaced approximately 16 to 20 percent of essential habitat for wintering and breeding migratory aquatic birds.

In San Francisco Bay, the Spartina is competing with and hybridizing with native cordgrass and vegetating the Bay’s mudflats. It impacts shorebirds and the endangered California clapper rail. Infestations have not only displaced native flora, but have also caused sedimentation changes, invertebrate and algae population decreases on the Bay floor and the destruction of foraging sites used by marsh birds, shorebirds and other animals.

Economic Impacts

In its native habitat there are some economically beneficial uses for Spartina alterniflora because of its wildlife sustenance and bank restoration values. But, in its non-native habitat on the Pacific Coast there are several negative economic effects.

Increased sediment build-up caused by Spartina alterniflora may cause changes in water circulation patterns, reducing tidal flow and increasing flooding, which has serious economic implications.

The loss of mudflat habitat jeopardizes commercial oyster production, which is a $16 million industry in Willapa Bay. In Willapa Bay more than $500,000 per year is spent to control the plant’s spread. Additionally, changes caused by the plant could impact eco-tourism because it reduces access to beaches, fishing waters, bird watching locations and wildlife photography sites.

Control and Removal

Mechanical and chemical control methods have been used and biological control methods are being developed for Spartina alterniflora. Typically, mechanical control is used for smaller infestations and chemical control is applied to larger populations, but there is no standard control method for infestations.

Mechanical control consists of hand pulling digging or covering methods. Using shovels and hand clippers, removing the entire root-mat is typically successful with 1- to 3-year-old plants because of their less-developed root system. Sometimes using a large shovel can successfully remove circular bunches up to 15 feet in diameter. All plant remains must be removed from the site to prevent re-sprouting.

Covering the plants with an opaque mat deprives them of sunlight and hastens decomposition, which can be successful for circular bunches up to 10 feet in diameter. Black plastic or geotextile mats are typically used to create this light tight atmosphere and must be left on for two consecutive years.

Mowing Spartina alterniflora can also control growth, restrict seed set, and ultimately kill it. The plant must be mowed regularly throughout the growing season from spring to fall.

Glyphosate is the only herbicide currently labeled for Spartina alterniflora treatment in Washington, although success varies. Varied results might occur because the leaves have high salt and sediment levels that prevent the chemical absorption. Therefore, some people have experimented with wiping the plants before spraying, which is harder work but is effective.

In Washington and California scientists have found that a leaf-hopper insect, Prokelisia marginata, feeds on the sap of Spartina alterniflora and is capable of controlling it. Once released, these insects take 5 to 10 years to increase their population enough to cause significant damage to Spartina alterniflora, while causing minimal damage to native plants. The leaf-hopper insect is seen as an inexpensive, long-term and non-toxic way to control the plant. Experimental releases have been and will continue to be conducted.

Physical Description

Spartina alterniflora is a rhizomatous, perennial grass that grows 0.3 to 3 meters tall and has a leaf blade width of 0.6 to 1.5 centimeters. The plant tends to grow in clumps on salt marshes and tidal mud flats. Its underground, soil-binding stems continually spread and sprout new plants. Its stems are hollow and hairless, but the leaves have hairy ligules. Spartina alterniflora‘s nondescript flowers bud in crowded, two-to-three-inch-long spikes.

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